Sweatshirts are commonly worn over shirts and t-shirts. Sweatshirts are commonly used by runners during the winter or in cold environments. Sweatshirts are meant to be lightweight for flexibility when running or performing other athletic activities. Sweatshirts are commonly blended mostly with cotton to absorb moisture/sweat from doing activities. They are extremely comfortable and are typically worn as pullovers. Sweatshirts have variations such as cardigans, zip-up sweaters, hoodies, and fleeces.